The invention relates to an electric incandescent lamp comprising:
a translucent lamp vessel or envelope sealed in a vacuum-tight manner;
current supply conductors which enter the lamp vessel at a first end through its wall;
a frame having arc discharge conductors extending substantially longitudinally in the lamp vessel and insulators extending transversely thereto interconnecting these conductors;
a filament comprising several wound sections, which are kept taut beside each other by the frame, each end of this filament being connected towards the first end of the lamp vessel to a respective current supply conductor.
Such a lamp is known from British Patent Specification 2,050,693.
An incandescent lamp of this kind can be used inter alia for the illumination of photographic studios or film studios, as a theater lamp or as a projection lamp. The lamp is frequently a halogen incandescent lamp and is in this case provided with a lamp vessel of quartz glass or another glass having an SiO.sub.2 content of at least 95% by weight and with a halogen-containing inert gas.
In such an incandescent lamp, a discharge arc can occur at the end of its life when the filament burns through. A high current then starts to flow through the lamp, which may lead to overheating of the lamp vessel, as a result of which the lamp explodes. In order to avoid explosion, the lamp is operated in series arrangement with a fuse which may be incorporated in the lamp and which interrupts, when it becomes operative, the current circuit through the lamp. In certain lamp types, the current through the lamp is smaller, however, (for example 80 A) upon the occurrence of a discharge arc than the high current (for example 100 A) transiently flowing when the lamp is switched on. Due to its short duration, this high transient current is not harmful, in contrast with the lower arc current if it is of fairly long duration. This lower arc current renders it very difficult to choose a fuse which becomes operative at this lower arc current and does not become operative at the higher transient current.